file: Factor files_lookup_fd_locked out of fcheck_files

[ Upstream commit 120ce2b0cd52abe73e8b16c23461eb14df5a87d8 ]

To make it easy to tell where files->file_lock protection is being
used when looking up a file create files_lookup_fd_locked.  Only allow
this function to be called with the file_lock held.

Update the callers of fcheck and fcheck_files that are called with the
files->file_lock held to call files_lookup_fd_locked instead.

Hopefully this makes it easier to quickly understand what is going on.

The need for better names became apparent in the last round of
discussion of this set of changes[1].

[1] https://lkml.kernel.org/r/CAHk-=wj8BQbgJFLa+J0e=iT-1qpmCRTbPAJ8gd6MJQ=kbRPqyQ@mail.gmail.com
Link: https://lkml.kernel.org/r/20201120231441.29911-8-ebiederm@xmission.com
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/fs/file.c b/fs/file.c
index eb1e2b7220ac6a26c5798f51d903f816b8714cde..6a6b03ce4ad69f135864f76bc2323daeb00d2580 100644 (file)
--- a/fs/file.c
+++ b/fs/file.c
@@ -1158,7 +1158,7 @@ static int ksys_dup3(unsigned int oldfd, unsigned int newfd, int flags)
 
        spin_lock(&files->file_lock);
        err = expand_files(files, newfd);
-       file = fcheck(oldfd);
+       file = files_lookup_fd_locked(files, oldfd);
        if (unlikely(!file))
                goto Ebadf;
        if (unlikely(err < 0)) {

diff --git a/fs/locks.c b/fs/locks.c
index cbb5701ce9f37f92fd88788b6414d4752cbbcd7b..873f97504bddf78147ba2bbbd9e515b6287d60a7 100644 (file)
--- a/fs/locks.c
+++ b/fs/locks.c
@@ -2536,14 +2536,15 @@ int fcntl_setlk(unsigned int fd, struct file *filp, unsigned int cmd,
         */
        if (!error && file_lock->fl_type != F_UNLCK &&
            !(file_lock->fl_flags & FL_OFDLCK)) {
+               struct files_struct *files = current->files;
                /*
                 * We need that spin_lock here - it prevents reordering between
                 * update of i_flctx->flc_posix and check for it done in
                 * close(). rcu_read_lock() wouldn't do.
                 */
-               spin_lock(&current->files->file_lock);
-               f = fcheck(fd);
-               spin_unlock(&current->files->file_lock);
+               spin_lock(&files->file_lock);
+               f = files_lookup_fd_locked(files, fd);
+               spin_unlock(&files->file_lock);
                if (f != filp) {
                        file_lock->fl_type = F_UNLCK;
                        error = do_lock_file_wait(filp, cmd, file_lock);
@@ -2667,14 +2668,15 @@ int fcntl_setlk64(unsigned int fd, struct file *filp, unsigned int cmd,
         */
        if (!error && file_lock->fl_type != F_UNLCK &&
            !(file_lock->fl_flags & FL_OFDLCK)) {
+               struct files_struct *files = current->files;
                /*
                 * We need that spin_lock here - it prevents reordering between
                 * update of i_flctx->flc_posix and check for it done in
                 * close(). rcu_read_lock() wouldn't do.
                 */
-               spin_lock(&current->files->file_lock);
-               f = fcheck(fd);
-               spin_unlock(&current->files->file_lock);
+               spin_lock(&files->file_lock);
+               f = files_lookup_fd_locked(files, fd);
+               spin_unlock(&files->file_lock);
                if (f != filp) {
                        file_lock->fl_type = F_UNLCK;
                        error = do_lock_file_wait(filp, cmd, file_lock);

diff --git a/fs/proc/fd.c b/fs/proc/fd.c
index d58960f6ee524db7fbc7642a2b1424b272359bd3..2cca9bca3b3a3ff110e856368bbaa764fc0b2587 100644 (file)
--- a/fs/proc/fd.c
+++ b/fs/proc/fd.c
@@ -35,7 +35,7 @@ static int seq_show(struct seq_file *m, void *v)
                unsigned int fd = proc_fd(m->private);
 
                spin_lock(&files->file_lock);
-               file = fcheck_files(files, fd);
+               file = files_lookup_fd_locked(files, fd);
                if (file) {
                        struct fdtable *fdt = files_fdtable(files);
 

diff --git a/include/linux/fdtable.h b/include/linux/fdtable.h
index 10e75b4c30a43a77b0fce05af2f25ff385f4529a..87be704268d2692963beefa386c1340ec7a283c2 100644 (file)
--- a/include/linux/fdtable.h
+++ b/include/linux/fdtable.h
@@ -91,6 +91,13 @@ static inline struct file *files_lookup_fd_raw(struct files_struct *files, unsig
        return NULL;
 }
 
+static inline struct file *files_lookup_fd_locked(struct files_struct *files, unsigned int fd)
+{
+       RCU_LOCKDEP_WARN(!lockdep_is_held(&files->file_lock),
+                          "suspicious rcu_dereference_check() usage");
+       return files_lookup_fd_raw(files, fd);
+}
+
 static inline struct file *fcheck_files(struct files_struct *files, unsigned int fd)
 {
        RCU_LOCKDEP_WARN(!rcu_read_lock_held() &&